Process of and apparatus for the production of argon



Dec. 27, 1955 R. BECKER ET AL 2,728,205

PROCESS OF AND APPARATUS FOR THE PRODUCTION OF ARGON Filed June 20, 19502 Sheets-Sheet l q l i 2 15 WW F y- RaooLF BECKER Jena 0056' Na GIIERERATTO R15)! Dec. 27, 195 5 BECKER ETAL 2,728,205

PROCESS OF AND APPARATUS FOR THE PRODUCTION OF ARGON Filed June 20, 19502 Sheets-Sheet 2 33 32 31 i H L .2 L: 45 A 14! o 52 5 4 36 5J5 gLa A 5755 41 51 T 4 M &-47

nited States atent PROCESS OF AND APPARATUS FOR THE PRODUCTION OF ARGONRudolf Becker, Munich-Sella, and Johannes Wucherer, Pullach, Germany,assignors to Gesellschaft fuer Lindes Eismaschinen A. G.,Hoellriegelskreuth, near Munich, Germany Application June 20, 1950,Serial No. 169,111 Claims priority, application Germany June 20, 1949 5Claims. (Cl. 62-4122) This invention relates to a process of andapparatus for the production of argon, and more particularly relates tothe manufacture of nitrogen-free argon from an argon-oxygen-nitrogenmixture obtained during the twostage rectification of air.

It is already known to produce mixtures of oxygen having a high argoncontent by removing the nitrogen contained in a mixture of nitrogen andoxygen in the upper column of a two-stage rectification apparatus.Thereafter, the fraction of the oxygen which contains the argon and thehigher boiling fractions is reintroduced into the rectificationapparatus where it is separated into a higher boiling componentconsisting of oxygen and into a lower boiling component consisting of anargonoxygen mixture. This mixture may be further separated, if desired,in a further rectification column into an argon fraction having only aresidue of oxygen.

However, experience has shown that the withdrawal of theargon-containing oxygen fraction from the low pressure column of the airseparation apparatus affects detrimentally the further separation of theair. Accordingly, it has been proposed to improve the known process andto prevent interference with the separation of the air by withdrawingonly a portion of the oxygen-argon mixture at a higher point in therectification apparatus where the concentration of the oxygen amounts tobetween 90 and 98 per cent. While this known process interferes with theair separation process less than the first process, it is still notsatisfactory because only a small portion of the argon contained in aircan be recovered.

It is accordingly the principal object of the present invention toprovide an improved process of and apparatus for the production of argonfrom air whereby the major portion of the argon which is contained inthe air may be recovered.

A further object of the invention is to provide a process of andapparatus for the manufacture of argon from a mixture of gases obtainedduring the two-stage rectification of air which will not substantiallydisturb the rectification of air.

In accordance with the process of the invention it is possible torecover the major part of the argon content of the air contained in theair separation column by withdrawing an argon-oxygen-nitrogen fractionat a point in the low pressure column where oxygen and nitrogen arepresent in substantially comparable or equal concentration. Thereafter,the nitrogen is completely removed by rectification of theargon-oxygen-nitrogen fraction in a distillation column and byseparating the remaining argon-oxygen mixture in a separation columninto pure oxygen and pure argon. The rectification is carried so far inthe distillation column that, for example, the argon-oxygen mixtureevaporated at the bottom of the column contains only approximately 0.02per cent of nitrogen. On the other hand, it is also possible to reducethe concentration of the argon leaving the column with the vaporizednitrogen to a minimum by using a distillation column of ampledimensions. By means 2,728,205 Patented Dec. 27, 1955 ice of the processof the invention the argon contained in cases, it may be desirable toremove the oxygen from the argon-oxygen mixture by a known chemicalmethod.

In a preferred modification of the process of the invention the liquidoxygen fraction obtained in the separation column is utilized to producethe sprinkling liquid required for the distillation column. Thesprinkling liquid is obtained by indirect heat exchange with thenitrogen fraction condensing in the condenser coils. The evaporatedoxygen is then discharged in counter-current heat exchange with freshgas. It is also feasible to combine the two columns in a double columnof the type used in air separators. In this case the sump liquid of theupper column condenses the rising nitrogen fraction of the distillationcolumn. However, in order to limit the height of the apparatus and toreduce the cold losses the two columns are preferably disposed adjacentto each other and the sump liquid of the separation column consisting ofliquid oxygen, is delivered by a pump to the.

condenser of the distillation column.

In order that the operation of the air separator may not be affected inany way, the cold required for the separation is produced, in accordancewith the invention, by the expansion of highly compressed nitrogen whichis guided in a closed circuit. This is effected as follows. At first theheat developed during the compression of the highly compressed nitrogenis dissipated. Then'the nitrogen is pre-cooled in counter-current heatexchange with the expanded cold nitrogen whereafter the sump liquid ofthe distillation column is heated by the .precooled nitrogen which isthus liquefied. After further cooling in heat exchange with the oxygenevaporating in the sump of the distillation column, the liquefied nitrogen is expanded and delivered to the head of the condenser to producesprinkling liquid from the argon fraction contained in the separatingcolumn. There the nitrogen is evaporated in indirect heat exchange withthe argon fraction which condenses partially. The vaporized nitrogen isthen permitted to escape and is used for further cooling of theliquefied nitrogen under pressure before it is expanded.

The apparatus for carrying out the process of the invention consists oftwo rectification columns which may, for example, be provided withrectification plates. One

of the columns serves as a distillation column for the nitrogen to befirst removed while the other column is the separation column for theargon-oxygen mixture; The apparatus further includes a liquid pump fordelivering the sump liquid of the separation column (oxygen) to thecondenser of the distillation column, a countercurrent heat exchangerfor the nitrogen cooling circuit, a counter-current heat exchanger forthe separation prod nets with the crude mixture and associated valves.

For a better understanding of the invention reference is now made to theaccompanying drawings, in which:

Fig. 1 is a schematic diagram illustrating apparatus for carrying outthe process of the invention; and

Fig. 2 is a schematic diagram illustrating further apparatus forcarrying out a modified process in accordance with the invention.

The argon containing mixture to be separated contains substantiallyequal parts of nitrogen and oxygen and is withdrawn from the lowpressure column of an air separator not shown in the drawing. Thismixture is introduced into a counter-current heat exchanger 1 at apressure of about 7- atmospheres where it is cooled. The mixture thenpasses through coil 6 and is introduced substantially in the center 7 ofthe distillation column 2. Here the mixture is separated into anitrogen-free oxygen-argon fraction which collects in liquid form 3 atthe bottom of the distillation column and into a nitrogen fractioncontaining argon and oxygen residues; The latter fraction leaves thehead of the distillation column at 5, is expanded by valve 25 andreheated substantially to the temperature of the high-pressure nitrogenwhich enters the system. The heating takes place by heat-exchange withhigh-pressure nitrogen in nitrogen counter-current heat exchanger 8 orin the counter-current heat exchanger 1. A portion of the fraction may,if desired, be directed through the counter-current heat exchanger 1 ina direction opposite to that in which the crude or untreated argonmixture flows. Another portion of this fraction has previously beencondensed in the coils of condenser 4 and serves as sprinkling liquidfor the distillation column 2. The oxygen-argon fraction is Withdrawn at9 from the distillation column 2 and is first expanded by valve 1% andthen introduced at 24 substantially at the center of the separationcolumn 11. Here, the fraction is separated into anoxygen fraction whichcollects at the bottom of the'column at 12 and into an argon fractionwhich is removed at 14 as pure argon and is passed through thecounter-current heat exchanger 1 before being utilized. A portion of theargon vapors arriving at the head of. column 11 is condensed in thecoils 13 of the condenser 27 and serves as sprinkling liquid for theseparation column. The'sump liquid 12 of the separation column 11 isdelivered by pump 15 having a motor 16 to the head of the distillationcolumn 2 where it is evaporated in indirect heat exchange withcondensing nitrogen. The evaporated oxygen is partly discharged at 21,passed through the crude gas counter-current heat exchanger 1 and heatedto approximately room temperature while another part is discharged at 22and introduced at 23 into the separation column.

The high-pressure nitrogen which serves for producing the required coldis passed after pre-cooling in the nitrogen counter-current heatexchanger 8, through coil 17 where it is liquefied. After furthercooling in the liquid oxygen by passing through coil 18 and throughsuper-cooling heat exchanger 19 the nitrogen is then passed throughexpansion valve 20 into condenser 27 of the separation column 11. Thenitrogen evaporated in the chamber 27 in heat exchange with the argoncon- (lensing in tubes 13 is returned into the closed circuit throughsuper-cooling heat exchanger 19 and through nitrogen counter-currentheat exchanger 8.

In accordance with a modification of the process of the invention thecold required for the separation process isproduced by a closed crudeargon circuit into which the; crude argon mixture to be separated isalso introduced and from which it is removed in a compressed state, andby means of highly compressed air. Both gases first serve in a condensedpre-cooled state to heat the separation: column whereby they areliquefied. After the thus formed liquid is expanded to vaporizationpressure it is employed to cool the upper part of the column whereby itis simultaneously evaporated. The vapors thus produced are brought intocounter-current heat exchange with compressed air to be pre-cooled orwith circulating. crude or untreated argon thereby to utilize their coldcontent. The compressed air, however, is only used to heat the sumpliquid of the distillation column and is thereby liquefied. Thereafter,the liquid is expanded and delivered to the head of the distillationcolumn for sprinkling purposes;

The modified separation process of the invention will now be describedby way of example with reference to Fig.

The crude or untreated argon to be separated which contains besidesargon approximately equal parts of oxyen. and' nitrogen is introduced at31 into a closed crude argon circuit. The mixture is compressed incompressor $2 with a circulating gas to about 4 atmospheres pressureabove atmospheric pressure. cooled by water cooler 33, pro-cooled incounter-current heat exchanger 34 and liquefied by the sump liquid 35 ofthe separation column 36 in the coil 46. A portion of the liquid thusformed is expanded by 'valve 37, vaporized by vaporizing coil 38 at thehead of separation column 36 and returned into the circuit throughcounter-current heat exchangers 6i) and 34. Another portion of theuntreated argon mixture is introduced in liquid form into thedistillation column 39 through valve 49 for the purpose of removing thenitrogen by rectification. The nitrogen driven off is discharged intothe atmosphere with the vaporized fraction of the liquid air introducedat 44 through valve 62 and the outlet 65 of counter-current heatexchanger 63.

The distillation column 39 is heated and vapors are formed from the sumpliquid 42 by a portion of the high pressure air which is condensed afterpro-cooling in the counter-current heat exchangers 63 and 56 in exchangewith escaping oxygen or nitrogen in the coil 41 in the liquidoxygen-argon mixture. The liquefied air is expanded through valves 43and 44' and introduced into distillation column 39 at 45. Here, theliquid air trickles over the vapors rising over the rectification platesof the distillation column 39 and washes theargon and oxygen contentthereof. liquid air is preferably evaporated and escapes through valve62 while a considerable part' of its argon content remains in the liquidphase and is thus recovered. The liquid air to be introduced at 45 intodistillation column 3? is super-cooled in heat exchanger 60 by coldcrude argon.

Another portion of the highly compressed air is used for the purpose ofheating the separation column in a coil 47 in addition to compressedcrude argon which condenses in coil 46. After liquefaction of the air incoil 47, the air is expanded by valves 48 and 49 and evaporated inspecial condenser pipes 52 at the head of separation column 36. This airis thereby utilized to condense the pure argon fraction to be recovered.The vaporized air is guided in the heat exchanger 63 in counter currentwith a portion of the condensed high-pressure air introduced at 64 anddistributed to the two counter-current heat exchangers 56 and as.

The oxygen-argon mixture obtained by rectification is withdrawn inliquid form at 51 from the bottom of the distillation column 39 andintroduced at 54 through expansion valve 53 into separation column 36'for further rectification. The oxygen component which collects in liquidform at the bottom of separation column 36 after rectification of theoxygenargon mixture introduced-therein, is first vaporized, then isdischarged in gaseous form at 55 and is brought into counter-currentheat exchange with highly compressed air in the counter-currentexchanger 56 and is discharged through outlet 66. In order to produce inthe separation column 36 simultaneously both argon of high purity aswell as oxygen of high purity a portion of the rising argon-containingoxygen is continuously withdrawn in gaseous form from the separationcolumn a few rectification plates above the level of the sump liquid.This fraction is branched 0d at 57 and introduced through valve 58 intothe expanded circulating argon at 61.

The pure argon produced at the head of separation column as is withdrawnin liquid form at 59 and vaporization of the accumulated liquid argonmay take place under pressure by suitable hot Vaporizers, not shown, and

discharged into suitable storage tanks, not shown; The

liquid may also be compressed to high pressure by pump- By excludingmechanically driven compressors and by utilizing a closed evaporationcircuit any contact with other liquids, such as lubricants and the like,and any contamination by other vapors or gases can be prevented. By theprocess of theinvention highly purified, absolutely dry gas can bedirectly produced The second process of the invention affords amongThereafter, it is The nitrogen fraction of the others the advantage thata large portion of the argon content of the highly compressed airutilized for the generation of cold is recovered during the process.

According to a further modification of the invention it may be expedientto omit separation columns 11 (in Fig. l) or 36 (in Fig. 2). In thiscase the oxygen may be removed from the argon-oxygen mixture chemicallyin a known manner instead of removing the oxygen in the separationcolumn.

The invention has been described with reference to a preferredembodiment and it will be understood that many variations andmodifications thereof may be resorted to Without departing from thescope of the invention as defined in the following claims.

We claim:

1. A process for the production of argon comprising the steps ofWithdrawing an argon-rich argon-oxygennitrogen fraction at apredetermined point of a two-stage air rectification process, the oxygenand nitrogen content of said fraction of gases being of substantiallyequal magnitude, rectifying said argon-oxygen-nitrogen fraction toremove the nitrogen substantially completely therefrom, separating theremaining argon-oxygen mixture into substantially pure oxygen andsubstantially pure argon by the application of cold, pre-coolingcompressed air and circulating it in a circuit, expanding the pre-cooledcompressed air in order to produce the required cold, indirectly coolinga portion of said argon-oxygen mixture by the expanded pre-cooled air,heating the separated substantially pure oxygen by the pre-cooledcompressed air, Washing out the argon from said argon-oxygen-nitrogenfraction by means of the expanded pre-cooled air, and discharging theair resulting from the washing out of the argon into the atmosphere inheat exchange with the compressed air.

2. A process as defined in claim 1 wherein oxygen containing a smallportion of argon is removed in gaseous form during the argon-oxygenseparation and fed into the crude argon circuit, thereby to recoversimultaneously argon and oxygen of high purity.

3. A process as defined in claim 1 wherein the produced pure argon iswithdrawn in liquid form, and is then vaporized under pressure.

4. A process for the recovery of argon from an argon oxygen nitrogenmixture comprising Withdrawing a gaseous argon rich oxygen nitrogenfraction from an air rectification device where the oxygen and thenitrogen content is of substantially the same magnitude, rectifying thesaid argon oxygen nitrogen fraction to efliect a complete removal of thenitrogen and thereafter separating the remaining argon oxygen mixtureinto its pure components, producing the cold required for the separationof the gas mixture by expansion of compressed circuitconducted precooledcrude argon and of precooled compressed air, while utilizing each ofsaid compressed gases for heating the separating column, therebycondensing said gases and using the same upon expansion from the fluidstate for the indirect cooling of the upper portion of the separatingcolumn, heating the fluid contained in the sump portion of thedistillation column by compressed air only, introducing the condensedair upon expansion into the upper portion of the distillation column forrinsing and washing argon, returning the vaporized crude argon upon coldexchange in counter-current heat exchanger into the circuit andreleasing the vaporized air while conducting the same in heat exchangewith compressed air.

5. In an apparatus for the recovery of argon from an argon-richoxygen-nitrogen mixture containing substantially equal parts of oxygenand nitrogen, a distillation column for the distillation of nitrogen, aseparation column for separating oxygen and argon from said mixture ofgases, means connecting said two columns for providing mutualcooperation thereof, a compressor and a cooler disposed in series tocompress and cool the initial gas mixture, a pair of counter-currentheat exchangers for pre-cooling compressed air in heat exchangecounter-current flow with expanded nitrogen obtained from saiddistillation column and with vaporized oxygen obtained from saidseparation column, a further counter-current heat exchanger connecteddownstream of said cooler for further cooling the initial gas mixture ina heat exchange counter-current flow with argon containing oxygenderived from said separation column, a first heating coil disposed inthe sump of said distillationcolumn and connected to said pair of heatexchangers to receive pro-cooled compressed air therefrom, a second anda third heating coil superposed in the sump of said separation column toheat the latter, said second coil being connected to said pair of heatexchangers to receive pro-cooled compressed air therefrom, said thirdcoil being connected to said further heat exchanger to receive thecooled initial gas mixture therefrom, a fourth and a fifth vaporizingcoil located at the top of said separation column to vaporize theliquefied gas mixture therein, said fourth coil having its outputconnected to one of said pair of heat exchangers to convey cooled airthereto flowing together with said expanded nitrogen, said fifthvaporizing coil being connected to the output of said third coil forcirculating a portion of the initial gas mixture.

References Cited in the file of this patent UNITED STATES PATENTS1,512,268 Barbet Oct. 21, 1924 1,527,639 Fonda Feb. 24, 1925 1,557,907Van Nuys Oct. 20, 1925 1,880,981 Pollitzer et al. Oct. 4, 1932 2,482,304Van Nuys Sept. 20, 1949

1. A PROCESS FOR THE PRODUCTION OF ARGON COMPRISING THE STEPS OFWITHDRAWING AN ARGON-RICH ARGON-OXYGENNITROGEN FRACTION AT APREDETERMINED POINT OF A TWO-STAGE AIR RECTIFICATION PROCESS, THE OXYGENAND NITROGEN CONTENT OF SAID FRACTION OF GASES BEING OF SUBSTANTIALLYEQUAL MAGNITUDE, RECTIFYING SAID ARGON-OXYGEN-NITROGEN FRACTION TOREMOVE THE NITROGEN SUBSTANTIALLY COMPLETELY THEREFROM, SEPARATING THEREMAINING ARGON-OXYGEN MIXTURE INTO SUBSTANTIALLY PURE OXYGEN ANDSUBSTANTIALLY PURE ARGON BY THE APPLICATION OF COLD, PRE-COOLINGCOMPRESSED AIR AND CIRCULATING IT IN A CIRCUIT, EXPANDING THE PRE-COOLEDCOMPRESSED AIR IN ORDER TO PRODUCE THE REQUIRED COLD, INDIRECTLY COOLINGA PORTION OF SAID ARGON-OXYGEN MIXTURE BY THE EXPANDED PRE-COOLED AIR,HEATING THE SEPARATED SUBSTANTIALLY PURE OXYGEN BY THE PRE-COOLEDCOMPRESSED AIR, WASHING OUT THE ARGON FROM SAID ARGON-OXYGEN-NITROGENFRACTION BY MEANS OF THE EXPANDED PRE-COOLED AIR, AND DISCHARGING THEAIR RESULTING FROM THE WASHING OUT OF THE ARGON INTO THE ATMOSPHERE INHEAT EXCHANGE WITH THE COMPRESSED AIR.